Devices of automation technology often have a service interface which, in particular, is implemented as a serial interface. Via this service interface, the user can configure the connected programmable controllers via a data processing device which is, for example, a portable computer, with the aid of a configuration program running on the data processing device.
However, it is also conceivable that measuring and control data are exchanged between the connected programmable controller and a data processing device via the service interface.
When a programmable controller is connected to the data processing device, the user must ensure that the correct communication interface is set by means of which the connection to the communication software is effected with the programmable controller. Otherwise, either no communication is possible or the user communicates unintentionally with a wrong programmable controller, also connected via a different communication interface, without noticing it. The communication can be effected for the configuration including parameterization, for the programming or for the diagnosis of the programmable controller or also for exchanging process data etc.
The configuration of decentralized devices by a serial USB interface is known, for example, from U.S. Pat. No. 7,412,544 B2, US 2002/0178295 A1 and EP 1 158 406 A2.
The systems use the standardized USB interface which provides a bit-serial bus in which individual bits of a data packet are transmitted successively. In this arrangement, the data transmission is symmetric via two twisted lines, in which one line transmits the data signal and the other one transmits a signal which is inverted thereto. Two other lines are used for supplying the connected devices with power. The devices connected to one another via a USB (universal serial bus) connection are coupled electrically in a point-to-point connection. The specification mandatorily requires a one-to-one correspondence of a USB device with a virtual interface, generated by means of interface drivers, for USB connections by means of the serial number of the connected USB device. This leads to a free, available virtual interface being selected by the interface driver by means of the serial number of the connected USB device when a USB device is connected so that a different interface is allocated to each USB device. This generation of virtual USB COM ports is described, for example, in U.S. Pat. No. 7,400,648 B2.
U.S. Pat. No. 7,577,735 B1 discloses a method for recognizing a target device on an interface connection of a multiplicity of virtual interfaces, in which a second interface connection of the number of virtual interfaces is allocated to a main device when the second interface connection is available.
U.S. Pat. No. 7,412,544 B2 discloses a method and system which allows a subscriber to use a remote USB device. For this purpose, a plurality of USB devices are coupled to a management module.
This automatic selection of interfaces in dependence on the instantaneous occupation of connections with USB devices which is uncontrollable for the user, leads to the user having to continuously manually change the interface settings in all applications which access such USB devices. Apart from this loss of comfort, the flexible generation of COM ports also harbors the risk of communicating unintentionally with wrong USB devices.